The present invention relates to improvements in coil spring making machines of the type disclosed in commonly owned U.S. Pat. No. 4,509,352 granted Apr. 9, 1985.
In a conventional coil spring making machine the wire is fed continuously by two advancing rolls and is intermittently severed by a knife which is arranged to move along an endless path intersecting the path of forward movement of the wire. The making of such flying cut is believed to be desirable and advantageous in order to increase the output of the machine. The knife is driven by a specially designed clutch which performs one complete revolution in response to each engagement. Consequently, the timing of the severing operation depends upon the timing of engagement of the clutch. A drawback of conventional machines is that the clutch is subject to extensive wear as a result of repeated engagement and disengagement so that the output is limited by the maximum permissible frequency of engagement and disengagement of the clutch.
Another drawback of conventional machines is that the advancing rollers are driven at a constant speed and, when the machine is designed to turn out coil springs with flat end convolutions, the wire treating tool (particularly a pitch selector tool) must be set in motion with a pronounced acceleration. This, too, limits the output of conventional coil spring making machines.
German Pat. No. 1,267,653 discloses a modified coil spring making machine wherein the wire is advanced in stepwise fashion. The means for driving the advancing means comprises a reciprocable input element which is movable along a straight path and drives the advancing rolls through the medium of two discrete one-way clutches. The transmission between the input element and the advancing rolls further comprises a first number of torque transmitting elements which operate between one of the clutches and one of the advancing rolls, and a different second number of torque transmitting elements which operate between the input element and the other advancing roll. The torque transmitting elements comprise gears and the arrangement is such that a first number of gears is interposed between the first clutch and the advancing rolls but a different second number of gears is interposed between the second clutch and the advancing rolls. One of the two sets of torque transmitting elements further comprises a reversing gear which ensures that the advancing rolls are driven in a direction to move the wire forwardly regardless of the direction of reciprocatory movement of the input element of the transmission.
A drawback of the machine which is disclosed in the German patent is that the play between the gears of the two sets of torque transmitting elements is compounded which reduces the degree of accuracy with which the wire is advanced toward the severing and pitch selecting tools. In other words, the overall or combined play between the elements of the first set of torque transmitting elements is different from the combined play between the elements of the second set of torque transmitting elements. This entails the making of coil springs having different dimensions.
Another drawback of the machine which is disclosed in the German patent is that severing of the wire takes place upon completion of the coiling or winding operation not unlike in a stamping machine. The cut must be made in one of several dead-center positions of the driving elemeent. The output of such machines cannot be increased beyond a predetermined (relatively low) value.